1. Field of the Invention
This invention relates to an optical recording medium especially suitable for application to a disc-shaped rewritable/reproducible optical recording medium.
2. Description of the Related Art
In recent data recording technologies, researches are being developed regarding optical recording systems. Optical recording systems can record and reproduce information signals without contacting a recording medium, and can attain higher recording densities as ten times or more as that those of magnetic recording systems. Additionally, optical recording systems have a number of advantages, including the availability for use with any type of memory such as reproduction-exclusive type, additional recording type and rewritable type. Thus, the optical recording systems are expected to be widely usable in industrial purposes and home-base purposes as a recording system that enables realization of inexpensive, large-capacity files.
Among those optical recording systems, optical magnetic discs and phase-versatile optical discs, for example, cope with rewritable memory modes. Optical magnetic discs are configured to locally heat a recording film made of a magnetic material to or above a Curie point or a temperature compensation point, thereby to decrease the coercive force of the recording medium, then apply an external recording magnetic field, thereby to change the magnetic orientation of the recording medium, and record information signals, or magnetically read out information signals. On the other hand, phase-versatile optical discs includes a recording film made of a phase-versatile material in which changes between a crystalline state and an amorphous state reversibly occur, and are configured to heat the recording film by irradiation of laser light, for example, thereby cause a change in phase in the recording film to record/erase information, or optically read out information signals.
As a conventional phase-versatile disc, DVD-RW (Digital Versatile Disc-Rewritable) is known and being spread. The format of DVD-RW is shown below.
Wavelength of light: 650 nm
Numerical aperture of the optical system lens:
Capacity: 4.7 GB
Track pitch: 0.74 xcexcm
Reflectance: 18 through 30%
Modulation: 60% or more
Resolution: 15% or more
Linear velocity: 3.49 m/s
Repeatable recording frequency: 1000 times or more
Address: LPP system (a system that obtains it from a pre-pit provided on a land)
In order to realize such a phase-versatile optical disc under that regulation (specifically, DVD-RW), AgInSbTe-series materials are used as phase-versatile materials, and Al alloys are used as materials of reflection films.
The conventional phase-versatile discs, however, merely cope with recording with the linear velocity of 3.49 m/s, further improvements in recording speed and reproducing speed are demanded. When an improvement of the linear velocity is tried toward realization of high-speed recording and high-speed reproduction, the following problem will occur. That is, recording or reproduction of information signals at a higher linear velocity than the conventional linear velocity (3.49 m/s (equal speed)) will invite an increase of jitters and decrease of the modulation. Therefore, practically acceptable recording characteristics could not be obtained.
It is therefore an object of the invention to provide an optical recording medium capable of preventing an increase of jitters and a decrease of the modulation even at a linear velocity higher than 3.49 m/s, and thereby ensuring practically acceptable recording characteristics.
According to the first aspect of the invention, there is provided an optical recording medium comprising:
a substrate having corrugated and ridge-and-concavo-convexgroove tracks on one major surface thereof; and
a first dielectric film, phase-versatile recording film, second dielectric film and reflection film that are sequentially stacked on one major surface of the substrate,
the phase change-versatile recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AgPdCu alloy material,
in the GeInSbTe alloy material forming the phase change-versatile recording film, content of Ge being in the range from 1 weight % to 6 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.4 times to 3.0 times, and in the AgPdCu alloy material forming the reflection film, content of Pd being in the range of 0.9 weight % to 1.5 weight %, and content of Cu being in the range of 0.9 weight % to 1.1 weight %,
depth of the furrow on the substrate having the groove tracks being in the range from 30 nm to 40 nm,
distance between two adjacent boundaries at opposite sides of the furrow being in the range of 0.27 xcexcm to 0.33 xcexcm,
amplitude of the corrugation being in the range of 30 nm to 35 nm at 0-peak;
thickness of the first dielectric film being in the range of 65 nm to 80 nm, thickness of the phase change-versatile recording film being in the range of-12 nm to 18 nm, thickness of the second dielectric film being in the range of 12 nm to 20 nm, and thickness of the reflection film being in the range of 80 nm to 160 nm.
According to the second aspect of the invention, there is provided an optical recording medium comprising:
a substrate having corrugated and ridge-and-concavo-convex groove tracks on one major surface thereof; and
a first dielectric film, phase-versatile recording film, second dielectric film and reflection film that are sequentially stacked on the one major surface of the substrate,
the phase change-versatile recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AlCu alloy material,
in the GeInSbTe alloy material forming the phase change-versatile recording film, content of Ge being in the range from 1 weight % to 6 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.4 times to 3.0 times, and in the AlCu alloy material forming the reflection film, content of Cu being not more than 1.5 weight %,
depth of the furrow on the substrate having the groove tracks being in the range from 30 nm to 40 nm,
distance between two adjacent boundaries at opposite sides of the furrow being in the range of 0.27 xcexcm to 0.33 xcexcm,
amplitude of the corrugation being in the range of 30 nm to 35 nm at 0-peak;
thickness of the first dielectric film being in the range of 65 nm to 80 nm, thickness of the phase change-versatile recording film being in the range of 12 nm to 18 nm, thickness of the second dielectric film being in the range of 12 nm to 20 nm, and thickness of the reflection film being in the range of 80 nm to 160 nm.
In the present invention, wavelength of light irradiated onto the phase change-versatile recording film of the optical recording medium upon recording or erasing information signal on or from the optical recording medium is typically in the range of 650 through 665 nm, approximately, and more specifically about 655 nm, taking compatibility with conventional recording/reproducing apparatuses into consideration.
In the present invention, numerical aperture of the lens in the optical system used upon recording or erasing information signals on or from the optical recording medium is typically in the range from 0.64 to 0.66, and numerical aperture of the lens in the optical system used upon reproducing information signals is typically in the range from 0.59 to 0.61. More specifically, numerical aperture of the lens in the optical system used upon recording or erasing information signals on or from the optical recording medium is approximately 0.65, and numerical aperture of the lens in the optical system used upon reproducing information signals is approximately 0.60.
In the present invention, the recording linear density in the optical recording medium is typically in the range from 0.2638 xcexcm to 0.2694 xcexcm per bit, and more specifically, the recording linear density in the optical recording medium is 0.267 xcexcm per bit.
In the present invention, the first dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction to the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 is used as the material of the first dielectric film.
In the present invention, the second dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction of the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 is used as the material of the first dielectric film.
In the present invention, the optical recording medium is a rewritable optical recording medium using a phase-versatile material as the recording film. Specifically, it may be DVD+RW (Digital Versatile Disc+Rewritable).
According to the optical recording medium having the above-summarized configuration according to the invention, the phase change-versatile recording film in the optical recording medium is made of a GeInSbTe alloy material; the reflection film is made of an AgPdCu alloy material or AlCu alloy material; the GeInSbTe alloy material forming the phase change-versatile recording film contains Ge in the range from 1 weight % to 6 weight %, In in the range from 2 weight % to 6 weight %, and Sb in the range from 2.4 times to 3.0 times of Te; the AgPdCu alloy material forming the reflection film contains Pd in the range from 0. 9 weight % to 1.5 weight % and Cu in the range from 0.9 weight % to 1.1 weight %; depth of each groove of the groove tracks on the major surface of the substrate is in the range from 30 nm to 40 nm; distance between two boundaries, among boundaries between lands and grooves of the groove tracks, is in the range from 0.27 xcexcm to 0.33 xcexcm; thickness of the first dielectric film is in the range from 65 nm to 80 nm; thickness of the phase change-versatile recording film is in the range from 12 nm to 18 nm; thickness of the second dielectric film is in the range from 12 nm to 20 nm, and thickness of the reflection film is in the range from 80 nm to 160 nm. This configuration can prevent deterioration of jitters and a decrease of the modulation even when the linear velocity is increased upon recording and/or erasing information signals, and thereby ensures sufficient recording characteristics in the optical recording medium.